1. Field of the Invention
The invention relates to a method of extracting tobacco alkaloids from tobacco. In particular, the invention relates to a method with which nicotine is extracted from tobacco.
2. Description of the Prior Art
The extraction of tobacco alkaloids from tobacco has been known for a long time in the art. Extractive methods using organic or aqueous solvents play an important part therein. In particular, the objective of various processes is the extraction of nicotine using such organic or aqueous solvents. The disadvantages of these methods is that the extraction is nonspecific and varying amounts of flavours are extracted from the tobacco along with the nicotine.
In addition, such extraction methods also have a negative effect on the structure of the tobacco and influence in undesirable manner the flavour of the smoke arising when such tobacco burns. Separation of the extracts obtained in the extraction and subsequent recombination of the fraction containing the flavours with the tobacco is very complicated.
Tobacco alkaloids, in particular nicotine, can be extracted selectively using solvents in the supercritical state. For this purpose, carbon dioxide has preferably been used. In German patent specification 2,043,537 a method is described in which nicotine is extracted from tobacco by means of CO.sub.2 in the supercritical state. The separation of the nicotine from the extract can be achieved either with sorbents or by expanding the extract mixture. Due to the relatively poor solubility of nicotine, long extraction times are necessary. They have disadvantageous effects on the smoke flavour of the subsequent burning tobacco when smoked.
German patent specification 2,142,205 describes a multistage method for removing nicotine from tobacco. Firstly, the flavours are extracted from dry tobacco with carbon dioxide in the supercritical state. Thereafter, the tobacco is brought into contact with moist carbon dioxide in the supercritical state, nicotine being extracted thereby. In the third method step the tobacco is again mixed with the flavours which were extracted in the first step. As in the method described above, the long process times lead to impairment of flavour and prevent an economic process.
To reduce the coextraction of flavours in the denicotinizing, a mixture of nitrogen and carbon dioxide under supercritical conditions can be used for the extraction (German Offenlegungsschrift 3,334,736). In German Offenlegungsschrift 2,844,781 it is proposed to increase the effectiveness and specificity of the extraction step by a combination of a gaseous (carbon dioxide) and a liquid (ethanol) component. These methods also have the disadvantage that due to the low solubility of nicotine in supercritical carbon dioxide, process times of several hours are required and these are contrary to an economic application of this extraction method. The extraction by the methods indicated above moreover leads to considerable losses of tobacco quality and smoke flavour.
EP-A 0 280 817 describes a method of extracting nicotine from tobacco and tobacco mixtures using supercritical or liquid extraction agents. The tobacco is brought into contact with extraction agents, inter alia also with carbon dioxide, to extract nicotine and also other tobacco ingredients. The nicotine is separated from the extract by passing the latter through a vessel containing a non-volatile acid or a salt of said acid. The flavour components pass through said vessel together with the extraction agent whilst the nicotine is chemically bonded in the vessel to the acid or the salt and thereby separated from the carbon dioxide.
A disadvantage of the method disclosed in EP-A 0 280 817 resides in that the non-volatile acid or salt of said acid necessary for bonding the nicotine must be attached to suitable carrier materials, for example shells of caco beans. In addition, the treatment vessels, in particular the pressure vessels, must be made very large because for separating the nicotine from the extract the acid or its salt (and thus also the necessary carrier materials) must be used in a ratio of at least 1:1, preferably however &gt;1:1.
In EP-A 0 280 817 it is moreover stated that the non-volatile acids suitable for separation of the nicotine from the extract by chemical bonding must not be soluble in the extraction solvent used under the extraction conditions. Consequently, salts of non-volatile acids having a particularly low solubility are especially preferred. This is apparently intended to avoid acid or salt being able to leave the separating vessel and penetrate into the extraction cycle.